The present invention relates to steam turbine speed control systems in general, and more particularly to a pair of concurrently operable electronic controllers which are coupled together to functionally cooperate in controlling the turbine acceleration primarily during turbine start-up operations in accordance with calculated present and anticipated rotor stresses, monitored differential temperatures from predetermined regions of the steam turbine, a number of predetermined critical speed zones and a predetermined heat soak speed.
It is well known that there are an increasing number of older steam turbine power plants which are being utilized in cyclic duty operation for stabilizing immediate power demand requirements of power system grids. In this capacity, the steam turbine may be repeatedly cycled between turning gear and synchronization speed, at times, frequently during normal daily power plant operation. A majority of these older steam turbine power plants do not have the benefit of a modern, sophisticated automatic turbine control system to enhance the prevention of deleterious conditions from occurring as a result of these frequent start-up and loading operations. Rather, most of the start-up procedures for these older power plants rely heavily on operator experience and awareness. For this reason, there has been an increase in interest in modernizing the speed control systems of certain types of older steam turbine plants, especially those utilized for cyclic duty.
In most cases, modernization of the turbine speed control systems does not entail merely replacing the older system with one of the sophisticated automatic turbine control system models because of the problems which are presented as a result of this replacement. An example of these problems include interfacing the new control system to the older turbine model for which it was not designed, training the plant operators to effectively and efficiently operate the new control system which generally include advanced control strategies usually incorporating digital computer control techniques, and absorbing the costs associated with parts, installations and testing thereof. Evidently, modernization cannot be handled this simply. Rather, a more acceptable retrofit approach, one which is more likely to satisfy most utilities, may be to offer a replacement which is more specifically designed to interface with their older steam turbine system and which provides more automatic and supervisory features to assist their power plant operators in more cautiously accelerating the turbine speed during the frequent start-up operations normally associated with turbine cyclic duty performance. Such a system is disclosed in the specification to follow.